The studies outlined in this proposal have as their ultimate goal the elucidation of the functions of eosinophils. Two approaches to this goal are planned. First we will utilize antiserum to eosinophils to ablate these cells from guinea pigs and we will analyze the effects of eosinophil deficiency on hypersensitivity reactions and other biological phenomena in which eosinophils are thought to play a role, such as normal fertility, antibody formation, and resistance to parasitic infections. Second, we will isolate eosinophil granules and purify from them the material composing the central crystalline core of the granule. This material is unique to eosinophils and may be responsible for the specific functions of the cell. The physiochemical and biological properties of this substance will be analyzed. The knowledge gained from these experiments may enable us to determine the specific functions of eosinophils not shared by neutrophils and thus to define the role of this cell in the inflammatory process and in the maintenance of normal health.